Autozeroing techniques are used in the prior art to control offsets in MOS circuits. In these techniques the offset in a MOS circuit is sampled and then used to zero out the offset. These techniques become more difficult as circuit speeds increase especially if adequate noise performance is to be attained. For bipolar circuits there are trimming or calibration techniques, but these are of limited usefulness for thermally induced errors that can change fairly rapidly.
What are needed are circuits and methods to limit the errors caused by thermally induced offsets or threshold shifts in comparators or folding amplifiers. In particular these circuits and methods are needed for flash analog to digital converters (ADCs) or folding ADCs in which a bank of comparators or folding amplifiers have their thresholds distributed across the entire input range. Those circuits at the top or bottom of the input range have their inputs driven below or above their thresholds a majority of the time, producing asymmetric power dissipation in their input stages, which causes thermally generated offset voltages in the circuits, reducing their accuracy and performance. This is particularly a problem for very high speed ADCs where high power densities are required to obtain the desired speed. The embodiments of the present disclosure answer these and other needs.